Vehicle periphery monitoring apparatus including a human body detector according to the background art extract information concerning a target object, such as a pedestrian or the like, who might possibly come into contact with the vehicle, which incorporates the apparatus therein, from images around the vehicle that are captured by two infrared cameras. The extracted information is presented to the driver of the vehicle.
Such a vehicle periphery monitoring apparatus detects, as a target object, a high-temperature area in images around the vehicle, which are captured by a pair of left and right infrared cameras (stereoscopic cameras), calculates the distance up to the target object by determining parallax between objects in the left and right images, detects a target object that could affect the travel of the vehicle from the direction in which the target object moves and the position of the target object, and outputs a warning (see Japanese Patent No. 3970876).
Japanese Patent No. 3970876 discloses a technique for detecting a head candidate for a target object, and for deciding whether or not the target object is a human body or a man-made structure, by determining whether the detected head candidate is larger than the lateral width of a human head (head width).
Detecting the distance between the installed positions of the two cameras and the target object based on parallax, as disclosed in Japanese Patent No. 3970876, is disadvantageous in that costs are increased because of the two installed cameras. Further, such a technique requires a complicated installation process including strict adjustment of optical axes of the cameras.
Another technique for eliminating the above disadvantages is disclosed in Japanese Laid-Open Patent Publication No. 2007-213561. According to the technique disclosed in Japanese Laid-Open Patent Publication No. 2007-213561, a single infrared camera, which is installed on a vehicle, is used to capture at least two images (two frames) of a target object near the vehicle within a certain time interval. A change in the size of a present image of the target object from the size of a previous image becomes greater as the relative speed between the target object and the vehicle, which incorporates a vehicle periphery monitoring apparatus therein, becomes higher. A target object, which is present in front of the vehicle, reaches the vehicle in a shorter time as the relative speed between the target object and the vehicle becomes higher.
Consequently, it is possible to monitor the periphery of the vehicle by estimating the time in which a target object reaches the vehicle, from the rate of change of the size of the target object in images that are captured within a given time interval.
According to the technique disclosed in Japanese Laid-Open Patent Publication No. 2007-213561, since a single infrared camera is used, the cost of the apparatus is lower than if two cameras are used, and therefore the apparatus can be installed on a vehicle at a reduced cost.
Documents according to the background art, which are relevant to the present invention, include Document 1, “Report on the Investigation of Japanese Body Frames, Measured from 1978 to 1981,” Ministry of Economy, Trade and Industry (Ministry of International Trade and Industry), Agency of Industrial Science and Technology, Japanese Standards Association (1984), and Document 2, “Measured Data of Japanese Human Bodies, Measured from 1992 to 1994,” Research Institute of Human Engineering for Quality Life (HQL).